In order to treat obesity, conventional surgical procedures involve attempts to either (1) restrict food intake into the body via a restrictive bariatric procedure or (2) divert the peristalsis of a person's normal food intake past the small intestine to decrease caloric absorption via a malabsorptive bariatric procedure. There also exists combined procedures in which both of the aforementioned techniques are employed jointly.
Restrictive procedures have encountered more success than malabsorptive ones, with the latter resulting in severe nutritional deficiencies in some cases. In restrictive procedures, the goal is to construct a passageway from the upper portion of the stomach to the lower portion, thereby preventing the stomach from storing large amounts of food and slowing the passage of food from the esophagus to the small intestine. Such a surgery results in the formation of a small pouch on the superior portion of the stomach near the gastroesophageal junction. In the beginning, the formed pouch holds approximately one ounce of food, but later distends to store two to three ounces. The lower outlet of the pouch is approximately one-half inch in diameter or smaller. The pouch diverts the passage of food to the lower portion of the stomach, thus avoiding storage of food in the stomach itself. When the pouch is full, it stimulates a feeling of satiation as well.
Purely restrictive operations for obesity include adjustable gastric banding (AGB) and vertical banded gastroplasty (VBG). These processes do not affect the digestive process. In AGB, a hollow silicone rubber band is placed around the stomach near its upper end, creating a small pouch and a narrow passageway into the rest of the stomach. The band is then inflated with a saline solution through a tube that connects the band to an access port located subcutaneously. It can be tightened or loosened over time to modify the size of the passage by increasing or decreasing the quantity of saline solution. Similarly, VBG utilizes rubber bands but also uses staples to create a small stomach pouch. The procedure involves puncturing the stomach to create a pouch that is not subject to the manual regulation observed in AGB.
In a malabsorptive bariatric procedure, an intestinal bypass is performed resulting in the exclusion of almost all of the small intestine from the digestive tract so that the patient absorbs a smaller amount of calories and nutrients. An example of a malabsorptive procedure is biliopancreatic diversion (BPD), in which about three-fourths of the stomach is removed in order to restrict food intake and decrease stomach acid production. The effect of this procedure is to alter the anatomy of the small intestine via the formation of an alimentary limb that diverts the passage of food past the first portion of the small intestine, including the duodenum and jejunum, and thereby prevents some of the bile and pancreatic juices from digesting some of the ingested food.
Combined operations are the most common bariatric procedures performed today. They restrict both food intake and the amount of calories and nutrients the body absorbs. An example of a combined procedure is the Extended (Distal) Roux-en-Y Gastric Bypass in which a stapling creates a small (15 to 20 cc) stomach pouch completely separated from the remainder of the stomach. The remainder of the stomach is not removed. The outlet from this newly formed pouch empties directly into the lower portion of the jejunum, which decreases caloric absorption. This connection is made by dividing the small intestine just below the duodenum and attaching the lower portion of the jejunum to the newly formed stomach pouch. The other end is connected into the side of the Roux limb of the intestine creating the “Y” shape that gives the technique its name.
There is ample evidence that gastric pouch size is a key factor influencing weight loss after bariatric surgery. There have been reports of an inverse relation between pouch size and excess weight loss; in other words, a smaller pouch will lead to greater weight loss. There is a limit to the minimum dimension, however, for health and safety reasons. Efforts to standardize small pouch size for all patients are important to the success of surgical therapy for morbid obesity.
The size of the pouch is important to the outcome of the procedure for AGB, VBG, or Roux-en-Y. Indeed, the AGB patients require a weekly visit to adjust the size of the pouch for maximum efficacy. Generally, there has been an inability to measure accurately and reproducibly the size of the gastric pouch, although a number of attempts have been made. Some researchers have used intraoperative measurement of pouch size with injected saline through a nasogastric tube before stapling of the stomach. Balloon catheters attached to a nasogastric tube and inflated with fluid have also been used. Nevertheless, the vast majority of bariatric surgeons currently estimate the pouch size using a visual estimate (i.e., transecting the stomach a specific distance for the gastroesophageal junction or between the second and third branches of the left gastric arterial cascade). Postoperatively, radiographic methods have been employed to approximate a three-dimensional pouch size volume from a two-dimensional filled contrast pouch.
The most commonly used method for studying the size and distensibility of hollow organs includes a balloon mounted on a catheter with impedance electrodes for measurement of the cross-sectional area in the middle of the balloon along with the balloon pressure (referred to as impedance planimetry). The distensibility of the organ is derived from computation of parameters such as tension, strain, cross-sectional area distensibility, and compliance (ΔCSA/ΔP) where ΔCSA denotes the change in cross-sectional area and ΔP denotes the change in pressure. Tension is computed using Laplace's law in the form T=ΔP*r where ΔP and r are the transmural pressure and the luminal radius of the organ, respectively.